1. Field of the Invention
The present invention relates to a receiver and, more particularly, to earphones and a receiver configured to make a cord of earphones or headphones function also as an antenna.
2. Description of the Related Art
With portable FM receivers, a technology called an earphone antenna is known in which an earphone (or a headphone) cord is made function also as an antenna of each portable FM receiver. This technology makes it unnecessary for an FM broadcast listener to pull out a rod antenna of the listener's portable FM receiver. Therefore, each portable MF receiver user can listen to FM broadcasts in a crowded train, for example, without causing nuisance.
Terrestrial digital television broadcasting is hardly affected by ghost signals, so that a portable receiver can be configured or a mobile phone can incorporate a terrestrial digital television broadcast receiver circuit. In these examples, making the earphone code function also as the receiver antenna allows the simple and convenient viewing of television broadcasts.
If the earphone antenna is used on the mobile phone incorporating a terrestrial digital television broadcasting receiver circuit, the earphone antenna is configured as shown in FIG. 3, for example.
To be more specific, referring to FIG. 3, reference numeral 10 denotes stereo earphones, reference numeral 20 denotes monaural earphones, and reference numeral 30 denotes a mobile phone. Each earphone unit is connected to an earphone plug with a lead wire formed by a cord, an intermediate unit 13, and a cable 14. In the stereo earphones 10, a left-channel earphone unit (an electroacoustic transducer) 11L and a right-channel earphone unit (an electroacoustic transducer) 11R are connected to the intermediate unit 13 with cords 12L and 12R, respectively and the intermediate unit 13 is connected to an earphone plug 15 with a cable 14.
In this case, the cords 12L and 12R are each a two-core signal conductor. These cords 12L and 12R act as the effective part of the broadcast receiver antenna. The intermediate unit 13 has coupling capacitors C11 and C12 and high-frequency choke coils L11 and L12.
Further, the cable 14 is formed by combining a coaxial cable 14A and two cables 14L and 14R into a single cable. The earphone plug 15 has 10 terminals (or contacts) A through J. It should be noted that, as will be described later, the mobile phone 30 has an earphone jack 31 corresponding to the earphone plug 15. Terminals A through J of the earphone plug 15 and the earphone jack 31 are standardized and therefore common among manufacturers.
One ends of the earphone units 11L and 11R are lead to the intermediate unit 13 through the cord 12L or 12R to be commonly connected in the intermediate unit 13 and further connected to terminal A of the earphone plug 15 through the center conductor of the coaxial cable 14A. The other ends of the earphone units 11L and 11R are lead to the intermediate unit 13 through the cord 12L or 12R and is connected terminals D and E of the earphone plug 15, respectively, through the high-frequency choke coils L11 and L12 and the cables 14L and 14R.
Further, the capacitor C11 is connected to between one and the other of the codes 12L and the capacitor C12 is connected to between the one and the other of the codes 12R. In the earphone plug 15, the shield of the coaxial cable 14A is connected to terminal J to connect terminal F with terminal J and, because the earphones 10 is for stereo, terminal C with terminal J.
The monaural earphones 20 are also configured in substantially the same manner as the right channel of the stereo earphones 10. It should be noted that, in the earphone plug 15, terminal F is connected to terminal J, but terminal C and terminal J are not connected to each other because the monaural earphones 20 are for monaural use.
As described above, the terminals A through J of the earphone plug 15 and the earphone jack 31 are standardized, the functions and uses thereof being specified as shown in FIG. 4.
To be more specific, of the terminals A through J of the earphone plug 15 and the earphone jack 31, terminal A is for the antenna and terminal C is for the detection whether the earphones are for stereo or monaural. Terminals D and E are for left and right channel audio signals. Terminal F is for the detection whether the earphone plug 15 is inserted into the earphone jack. Terminal J is for grounding. The remaining terminals B and G through I are reserved.
When the earphone plug 15 of the stereo earphones 10 is inserted in the earphone jack 31, the broadcast wave of FM broadcasting or terrestrial digital television broadcasting is received at the cord 12L and the cord 12R. The received broadcast wave signal is supplied to the mobile phone 30 along a signal line, from the cord 12L and cord 12R (or the cord 12L and the cord 12R to the capacitors C11 and C12), to the center conductor of the coaxial cable 14A to the terminal A of the earphone plug 15 and to the terminal A of the earphone jack 31.
It should be noted that, in the above-mentioned case, the shield of the coaxial cable 14A is connected to the ground of the mobile phone 30 through the terminal J of the earphone plug 15 and the terminal J of the earphone jack 31. Because the high-frequency choke coils L11 and L12 are connected to the codes 12L and the 12R at this moment, the received broadcast wave signal on the cords 12L and 12R will not leak to the terminals E and D of the earphone plug 15. Consequently, the FM broadcast or the terrestrial digital television broadcasting can be received.
Then, audio signals L and R on the left and right channels obtained from this reception of broadcast are supplied to the earphone units 11L and 11R along a signal line, from the terminals E and D of the earphone jack 31 to the terminals E and D of the earphone plug 15 to the high-frequency choke coils L11 and L12 and to the cords 12L and 12R. At this moment, a return path is formed, from the earphone units 11L and 11R to the cords 12L and 12R to the central conductor of the coaxial cable 14A to the terminal A of the earphone plug 15 to the terminal A of the earphone jack 31 to the high-frequency coke coil L35 and to the ground.
When the earphone plug 15 of the monaural earphones 20 is inserted into the earphone jack 31, the FM broadcasting or the terrestrial digital television broadcasting can also be received to allow the user to listen to the received broadcast through the monaural earphones 20.
It should be noted that, if the earphone plug 15 of the stereo earphones 10 is inserted in the earphone jack 31, the terminal C of the earphone jack 31 is grounded through the terminals C and J of the earphone plug 15; if the earphone plug 15 of the monaural earphones 20 is inserted in the earphone jack 31, then the terminal C of the earphone jack 31 is open. Therefore, the DC potential on the terminal C of the earphone jack 31 indicates whether the earphones connected to the earphone jack 31 are the stereo earphones 10 or the monaural earphones 20.
If the earphone plug 15 of the stereo earphones 10 or the monaural earphones 20 is inserted in the earphone jack 31, the terminal F of the earphone jack 31 is grounded through the terminals F and J of the earphone plug 15; if the earphone plug 15 of the stereo earphones 10 or the monaural earphones 20 is not inserted in the earphone jack 31, then the terminal F of the earphone jack 31 is open. Therefore, the DC potential on the terminal F of the earphone jack 31 indicates whether the stereo earphones 10 or the monaural earphones 20 are connected to the earphone jack 31.
As described above, according to the stereo earphones 10 and the monaural earphones 20 shown in FIG. 3, each of the stereo earphones 10 and the monaural earphones 20 can be used also as the antenna for receiving the FM broadcasting and the terrestrial digital television broadcasting.
The related-art documents include the following:    Japanese Patent Laid-open No. 2003-163529;    Japanese Patent Laid-open No. 2004-266434;    Japanese Patent Laid-open No. 2004-274356; and    Japanese Patent Laid-open No. 2005-64742.